The present invention relates generally to diagnostic systems for internal combustion engines, and more particularly to a diagnostic system for an internal combustion engine including a plurality of cylinder banks.
In general, internal combustion engines are controlled optimally in accordance with operating conditions of sensing targets which are determined based on information collected by sensors. Some engines include redundant systems for safety, in which a sensing target is monitored by a plurality of sensors. This redundant system leads to safe operation of the engine, even when there occurs a failure in one or more of the sensors. Such a fail-safe control system for an internal combustion engine is shown in a Published Japanese Patent Application No. H2(1990)-176141 (hereinafter referred to as “JP2-176141). In JP2-176141, the control system includes a redundant fail-safe system including a pair of accelerator opening sensors to sense an accelerator opening. When one of the accelerator opening sensors is damaged to output an incorrect signal because of its abnormality or failure, the failure is detected by comparison between the signals output by the two accelerator opening sensors.
Similarly, some of the control systems include a redundant fail-safe system including a pair of throttle position sensors (throttle angle sensors) to sense a valve opening (valve rotation angle) of a throttle valve for regulating the quantity of intake air flowing into cylinders. When one of the throttle position sensors is damaged to output an incorrect signal because of its abnormality or failure, the failure is detected by comparison between the signals output by the two throttle position sensors.